This invention relates to data storage disk drives and, more specifically, to improved clamping devices for clamping a disk or disk stack onto the hub of such a drive for holding and driving such hub and disks by utilizing a uniform distribution of force on the disk to retain its position relative to the hub, without causing disk warpage or other undue localized stresses.
In the assembly of a high-speed, high-capacity data disk drive, it is common to use magnetically recordable disks that are disk substrates coated with a magnetically recordable medium. Due to mass, energy and size design constraints and other design considerations, the disks are made of glass and, therefore, extremely fragile.
The disks are mounted along with spacer rings on a rotatable hub and clamped to the hub to form a disk stack. The clamping has been accomplished by attaching a clamp ring to the hub and tightening a plurality of screws to compress the surfaces of the spacer rings and glass disks into intimate frictional contact. The screws are torqued to substantially equal value. However, the loading of the screw tightening causes a concentration of force at discrete locations around the top of the disk pack. This leads to a non-uniform force distribution exerted on a disk stack necessarily requiring a larger force level on it to hold the disk stack in the desired position in relation to the hub.
Disk warp is commonly induced by non-uniform clamping forces. Disk warp causes non-uniform flight characteristics, such as flight height. Disk warps can cause read/write errors and may cause head crashes damaging the read/write head and/or the magnetically recordable and readable data storage disk. Although a disk may survive the large centrifugal force-loading, disk warp complicates the control of flight characteristics of read/write heads over the disk surfaces due to constantly varying flight height. At such high speeds, the read/write head can not respond quickly enough to insure high quality read/write signals and avoid head crashes.
Even a very minor crack in the disk may cause the disk to fail due to the large centrifugal forces generated by rotating the disk or disk stack at high speed, typically 10,000 to 15,000 revolutions per minute. These forces combine with the stresses in the glass near the stack to cause a disk to break.
A concentration of forces in a limited number of spots about the substrates will increase the likelihood of disk distortions created, such as warps. The creation of stress in one or more of the disks may be sufficient to cause a glass disk to crack and certainly will cause warping in both glass and metal disk substrates, further causing variations in the flight height of the read/write head which is a critical part of any magnetic disk drive.
One very serious problem caused by the warpage is radial track positioning error. An increase or decrease in axial height may cause a shift relative to the data track of as much as a ratio of from 1:8 to 1:10 times the axial height variance, causing improper head tracking of the data track.
Warpage is directly attributable to the number of screws used as point loading sources. The point loads can create not only the number of warps corresponding to the number of point loading sources, but multiple harmonics due to formation of a multiple of warps per point load.
It is an object of the invention to improve the reliability of data storage disk drives.
It is another object of the invention to fix the disks relative to the hub of a disk drive without subjecting a disk to force concentrations that cause deleterious effects in a disk.
It is a further object of the invention to utilize a substantially uniform force distribution in clamping disks in a disk stack.
It is an additional object of the invention to prevent disk breakage which can result from non-uniform clamping force distribution on a disk and disk stack.
It is a still further object of the invention to reduce or eliminate disk warp associated with the clamp force loading.
It is a still an additional object of the invention to improve the signal quality in reading and/or writing a magnetically recordable and readable disk with data.
In a data storage disk drive, one or more coated glass disks are alternated with a similar number of spacer rings to create a disk stack. This disk stack is positioned around a rotatable hub and clamped to the hub for revolution therewith. Glass disk substrates are preferred for a number of reasons; nevertheless, they are subject to cracking by the concentration of clamping forces at discreet points about a disk. Both metal, such as aluminum, and glass disks may be caused to warp by the point loading, which similarly effects the reliability of the system. The use of glass disks is the preferred embodiment, but it must be understood that the invention also addresses metal or other material disks.
In order to eliminate the clamping force concentrations, this invention provides a clamping assembly which engages the disk stack with a uniformly distributed clamping force.
Two ring-like structures are co-axially juxtaposed with a deformable ring disposed intermediate the rings. The bottom ring is engaged with the top member of the disk stack.
The top ring is attached to the hub by screws that, whenever tightened, force the top ring toward the hub, and thus force the top ring against the deformable ring and against the bottom ring.
The deformable ring is typically constructed of an external elastomeric or other deformable casing such as a thin metal outer casing and contains therein a liquid, gel or free-flowing powdered metal; under pressure, this free-flowing substance will spread the contents to conform to the members which are exerting forces thereon.
As the screws are tightened to create the clamping force required, the contents of the casing are squeezed: subsequently, as pressure is created, the pressure exerts forces on the bottom clamping ring which, in turn, transmits the force to the disk stack.
Sufficient uniform loading of the bottom clamping ring is generated to clamp and fix a disk stack relative to the hub.
By clamping a disk stack with a uniform force loading, the clamping does not introduce non-uniform forces to the disks, thereby not creating those stress concentrations which can cause cracking or disintegration of a disk and possibly a disk stack. Furthermore, any disk warp which is induced by non-uniform force clamping force loading is prevented.
This Summary of the Invention is provided to summarize the disclosure of the invention, however, this Summary of the Invention is not to be used to limit the invention in any manner.